Two competing models, structural and psychophysiological, have received the greatest amount of attention in the TMPDS/TMJS literature. Available research is equivocal and does not support the adequacy of either of these two models. Moreover the research does not permit definitive statements about the etiology, exacerbation, maintenance of symptoms, and consequently appropriate treatment. The studies are designed to experimentally evaluate, using sophisticated psychophysiological, radiographic, and dental assessment procedures, the contribution of psychological and structural factors to TMPDS/TMJS. In addition, the differential efficacy of structure and psychophysiological treatments for these patients will be assessed. The important question of the characteristics of patients (demographic, structural, and psychological) who benefit from the different treatments will be examined. The specific aims of the research are: (1) to demonstrate the effects of stress on the muscles of mastication on patients with and without radiographic findings of TMJ abnormalities; (2) to determine the differential efficacy of structural and psychophysiological treatments in comparison to placebo treatments for patients with and without positive radiographic findings; to determine the characteristics (demographic, psychological, structural) of patients who receive the most beneficial effects of the two treatments; and (4) to address the mechanisms by which each treatment achieves its positive effects, specifically the effects of muscular hyperactivity on the report of pain symptoms. The project has as its long-term research objectives the integration of psychophysiological evaluation of dental and radiographic assessment procedures. The health implications include increasing our understanding of the underlying biobehavioral mechanisms in TMPDS/TMJS order to facilitate decisions regarding the most appropriate treatment modality based on both psychological and structural evidence.